Apparatus for forming a thin film



DCC. 22, 1970 R SCHNElDER ETAL 3,549,334

APPARATUS FOR FORMING A THIN FILM Filed Deo. 26, 1967 f--Ll y INVENTORSI RUDOLF SCHNEIDER, OTT() COURT, UAI-TER MHSKY, GEDRG SPbTT, HERMANN SCHNELL, LUDWIG .DOTTINBRUCH, ULRICH CURTIUS, CLAUS HUI-PP.

BY r

` Hi'torney.:

United States Patent O Im. c1. Bind 1/22 U.S. Cl. 23-285 11 Claims ABSTRACT OF THE DISCLOSURE An apparatus for forming a thin film of a composition at the inside surface of a shell by means of a wiper helix, having a feed surface inclined under an angle between 100 and 175 in relation to the wiping surface of said helix and directed toward the outlet end of said shell to stabilize the distance of said wiping surface to said inside surface of said shell. Preferably the other corners of said helix are also faced or rounded to avoid deposits and incrustations of material.

This invention relates to a rotating wiper helix which Yis arranged in an apparatus for forming a thin lm of a composition to distribute said composition over the inner wall of a shell. Reaction and evaporator apparatuses of this type are used, for example, in the production of thermoplastic polycondensation products, especially materials of high viscosity.

Wipers previously in use, consisting of a helix made up of a band of rectangular or circular cross-section, required a great deal of force to drive the helix, especially when used with materials of higher viscosity, because the material tended to accumulate on the helix. There is also a risk that the helix might be deformed owing to its elasticity, and hence grind against the wall of the tube shell so that both the helix and the tube are prematurely worn down. Uniform distribution of the material over the wide wall of the shell which is of fundamental importance for the reaction or evaporation process, can then no longer be ensured. Zones in which only very slight movement of material occurs are thus formed when helices of conventional cross-section are employed, and the formation of these zones causes different parts of the treated material to undergo treatment for different lengths of time, so that a non-uniform end product is obtained. The incrustations and accumulations of material which occur at the same time can damage the helix and the outlet.

It has now been found that such wiper helices can be improved if the cross section of the band making up such helix is modied from the prior art configuration so as to provide a band cross-section having a chamfer edge on the forward end thereof directed toward the inside wall of the shell in which such helix is intended to operate.

yIt has also been found that the wedge-shaped gap formed when the profile of the wiper helix in the direction of feed has the surface in the direction along which the material travels through the shell inclined to the wiping surface of said helix at an angle y of between 100 and 175, preferably between 120 and 150; the material drawn into the gap between said inside surface of said shell and the wiping surface of said helix causes the helix to center itself, and uniformly distributes material over the inside surface on the shell without abnormal wear ice and tear of the helix and shell occurring, and requires much less force for driving the helix.

According to a special embodiment of the invention, the inclination of the chamfer of the helix may advantageously vary over the length of said helix. It is therefore possible to influence the length of time during which the material stays in a certain zone of the shell, which zone may, for example, be designed to be heated or more strongly heated than the rest of the shell or cooled. The present invention also provides for the helix band to be designed in such a manner between the surface of the helix remote from the Wall of the shell and the leading surface of said helix there is positioned and connected to both said surfaces a deecting surface, which is inclined at an angle of between and 170, preferably between and 150. This embodiment in addition reduces the amount of power required and helps to control the uniformity and thickness of the layer of material which has to be distributed. A special advantage of this embodiment however, is that it causes the helix to be automatically cleared. Previously, deposits and incrustations formed on the surfaces of said helix, but now part of material constantly flows over the inwardly directed surface of the helix if there is uniform rate of feed, so that no deposits can form. The distribution of material and length of residence in individual zones of the shell can also be regulated by varying the inclination of said dellecting surface over the length of the helix.

According to a further feature of the invention, the amount of force required and the friction generated between material and the helix can be still further reduced Iby providing only part of the surface of the helix directed toward the inner surface of the shell as the wiping surface and providing the remainder of this surface further removed from the inside surface of the shell than the wiping surface, for example a relief step can be provided, so that the helix has only a small wiping surface directed toward the wall of the shell. The helix may, of course, comprise an arrangement of several helices in known manner, or the different turns of the helix may have different pitches.

Reinforcing means may be arranged between the turns of the helix in known manner to stiffen said helix. Apparatus of this type are known which employ several helices one inside the other each of which serves to reinforce the others and to aid in mixing operations, the second helix has a greater pitch than the first one. The two helices have the same external diameters. This design may be used for mixing and conveying material but is not suitable for producing thin layers on the wall of the tube because the viscous material, which is conveyed in a relatively thin film along the inside surface of said shell, accumulates in the corners formed between the two helices in the direction of movement of the material. The material accumulated in these positions has a much greater period of residence than the material travelling forwards along the wall, so that uniform reacting or evaporation of the treated material is not achieved. Furthermore, the material, which becomes more viscous as a result of the treatment in the apparatus, tends to cake into these corners, and so disrupts the operation.

It has now been found, that this disadvantage can also be overcome according to a special embodiment of the invention, wherein the reinforcing means are further from the wall of the shell than the wiping surface of the helix, the distance preferably being constant over their whole length, and their pitch is in the same direction but greater than that of the helix.

It is obvious that reinforcing means arranged in adjacent flights of the helix may be staggered relative to each other. The distance of said reinforcing means from the wall therefore preferably so arranged that saidreinforcing means only just dips into the film of material so as to ensure that the material will ow round said reinforcing means, thus producing a cleaning action thereon. The pitch of `said reinforcing means should be chosen inv accordance with the viscosity of the material and may vary over the length of the helix to correspond to any `changes in Viscosity which `occur whereby to achieve a lower resistance. Furthermore, the shell and the helix, both may be heated or cooled so that the apparatus can be adjusted as far as possible to meet the requirements of the particular material or the particular process to be carried out.

It is especially advantageous if the `discharge end of the helix is positioned adjacent to `but not continuous with the discharge screw. This prevents deposits forming around the end of the helix, both on the helix itself and on the wall of the shell.` The discarge screw is preferably conical and in the form of a coreless helix at its wider end, that is,

the end adjacent to said wiping helix, in order to make use of the cleaning action of the material by allowing it to iiowround the helical part.

The apparatus is preferably arranged horizontally or at a slight inclination. In the case of materials of low viscosity or of liquids it may also be advantageous to arrange the apparatus vertically.

The present invention will now be explained with reference to the accompanying drawing in which:

FIG. 1 is an axial cross-section through the apparatus and FIGS, Zand 3 are cross-sectional profiles showing special forms of the helical band.

In FIG. 1,' a reaction shell lis provided with an inlet 2 for the composition to be treated, outlet 3 for the nongaseous component, and an outlet 4 for the gaseous component. The reaction tube is surrounded by a cooling or heating jacket 5 which has an inlet 6 for heating or cooling `medium and an outlet 7 for said medium. A helix 10, equipped with a drive means 9, Vis rotatably mounted in a lid 8. Obliquely placed reinforcing means 12 are arranged between the flights of thehelix. 10. Below the helix is a discharge screw 13 which directly follows but is discontinuous with the end of the helix 10. Partof the screw 13 has a core 21 and part 0f it is in the form of a coreless helix 22.

In FIG. .2, the helix 10, is provided with a wiping survface 15, which faces the shell wall 1. There is further a relief step 16, The helical band has a chamfer 17 whichV is inclined to the wiping surface at an angle 'y of 135 in this example. `The surface 18 of said `helix which is directed inwards has a deflecting surface 19 which is in- 4 What we claim is: 1. An apparatus for forming a thin film of a composition which comprises a shell with an inlet opening to feed said composition, an outlet opening to permit ,escape of the` produced -gaseous component, outlet Asurface is substantially normal/to said inner surface of said shell, a chamfer, third surface disposed between and connected to said first and second `surfaces which is inclined at an angle of 135 in this example to the surface 18. The reference numeral 20 indicates a leading surface. The distance a between the wiping surface 15 and the wall 14 is less than the distance b between the reinforcing means 12 and the wall 14. The cross-section of the reinforcing means 12 may be elliptical, oval or other shape such that it has substantially one surface.

To complete the Yhelical wiper of this invention there is an inwardly directed fourth surface 18 and there is also provided a fifth surface disposed between the leading surface 20 and the inwardly directed fourth surface 18 which is shown assurface 19 in FIGS, 2 and 3.

4The referred to surfaces are then-a first surface 15, a second surface 20, a third surface 17, a fourth surface 18 and a -fth surface 19. Y

In FIG. Y3, the inner surface 18 of the helix 10 is an arcuate surface V18.

clined with respect to said rst surface at an angle ,u between 100'ar1d175.

2. The apparatus according to claim 1, wherein said angle 'y varies over the length of said helix.

3. The apparatus according to claim, 1 wherein said helix includes a fourth surface substantially directed to the interior of said shell, a fifth surface disposed between and connected to said second and fourth surfaces and inclined with respect to said second surface at an angle between and 170.

4. The apparatus according to claim 1, wherein said angle varies over the length of said helix.

5. The apparatusaccording to claim 1, wherein said first surface comprises two substantially parallel levels, one of `which is awiping surface and the other of which is disposed further from the inside surface of said shell than Vsaid wiper, which levels are joined together by a step.

6. The apparatus according to claim 1, wherein said fourth surface is arcuate. e

7, .The apparatus according to claim 1, including reinforcing means between the turns of said helix spaced from said inside surface of said shell a distance greater than the distance said first surface is spaced from said inside surface.

8. The apparatus according to claim 7, wherein said reinforcing means have a rounded surface.

9. The apparatus according to claim 7, wherein said Voutlet means includes a cone housing with its end of larger diameter connected to said shell and a discharge screw rotatablyarranged coaxially to and inside of said vcone housing, the end of said discharge screw positioned to operate in relation to said helix.

10. The apparatus according to claim 9, wherein said outlet means includes an end part with a coreless helix, said coreless helix passing'over into avthread of said said discharge screw in the direction to the outlet opening.

11.` The apparatus according to claim 1, wherein said angle y is between 120 and 150.

References Cited UNITED STATES PATENTS JAMES H. TAYMAN, JR., Primary Examiner U.s. C1. X.R.

159-6; 165-94; l98-213; 15-`l04.l, 93, 246.5 

